1. Field of the Invention
The invention relates generally to the field of Positron Emission Tomography (PET). More particularly, the invention relates to PET detectors. Even more particularly, one implementation of the invention relates to tuning a PET detector.
2. Discussion of the Related Art
In current clinical PET cameras, there are 1000 or more photomultipliers (PMT) in the detector system. Even a less-complicated gamma camera has many dozens of PMTs. The output of one PMT can vary by 3–5 times from the next PMT for the same detected energy. Image quality and resolution are dependent on the proper equalization of all the PMT outputs; the equalization can be performed by adjusting (manually or electronically) the amplification gain of an amplifier following each PMT and/or by adjusting the high-voltage level supplied to each PMT so that the amplifier outputs for all the PMT are the same for the same energy detected in scintillation detectors. The conventional equalization process (photo-peak pulse-height tuning) for hundreds or thousands of PMTs is very tedious and time consuming. Furthermore, even after an equalization, a PMT output (gain) can change later with many environmental factors such as room temperature, patient load, short-term and long-term radiation exposure, time, etc. Furthermore, these gain changes are different for individual PMTs. A typical PET system-wide PMT-gain adjustment takes many hours (a long down time for a clinical camera), and it is usually performed once every few weeks or every few months. Hence, optimal image quality may not be achieved for all the patients between system equalizations. Furthermore, if one PMT suddenly produces undesirable results such as having gain drop significantly, say, at noon, all the patients imaged in the afternoon will be suboptimal (or useless) without any prior warning.
In sum, conventional PMT equalization methods suffer from several shortcomings, one of the most prevalent being the inability to equalize PMTs in a timely fashion so that the resulting images are more consistent in quality. The referenced shortcomings are not intended to be exhaustive, but rather are among many that tend to impair the effectiveness of previously known techniques concerning PMT tuning methods; however, those mentioned here are sufficient to demonstrate that methodology appearing in the art have not been altogether satisfactory and that a significant need exists for the techniques described and claimed herein.